An ultra wide band (UWB) radio communication system has been known which realizes power consumption and cost lower than those of radio communication systems that modulate continuous carriers and perform communication such as a cellular phone and a wireless LAN.
The UWB radio communication system is a radio communication system that discretely transmits and receives impulse signals and performs communication without using continuous carriers unlike the cellular phone. Since frequency spectra of the impulse signals are distributed in a wide band, the UWB radio communication is called Ultra Wide Band Impulse Radio (UWB-IR) communication and attracts attention as a radio communication system adoptable in a low-power sensor net system. The UWB-IR radio communication system adoptable in the low-power sensor net system is described in, for example, Lucian Stoica et al, “An Ultrawideband System Architecture for Tag Base Wireless Sensor Networks”, IEEE TRANSACTIONS ON VEHICULAR TECHNOLOGY, VOL. 54, No. 5, SEPTEMBER 2005, PP. 1632-1645 (hereinafter referred to as Non-Patent Document 1) and Lucian Stoica et al, “A Low-Complexity Noncoherent IR-UWB Transceiver Architecture With TOA Estimation”, IEEE TRANSACTIONS ON MICROWAVE THEORY AND TECHNOLOGY, VOL. 54, No. 4, APRIL 2006, PP. 1637-1646.
In the UWB-IR radio communication system, for example, a time width of an impulse signal is about 2 nano-seconds and an interval between impulse signals is about 30 nano-seconds. As a result, as described above, frequency spectra of impulse signals discretely transmitted are distributed in a wide band. In this way, since the impulse signal of the UWB-IR radio communication system has signal components in a wide frequency band, a receiver for the UWB-IR radio communication system needs to perform operations necessary in the wide frequency band. A frequency band of the Wideband Code-Division Multiple Access (WCDMA) radio communication presently used in cellular phones widely is about 5 MHz. On the other hand, a frequency band of the UWB-IR radio communication is about 500 MHz or more, which is about 100 times as wide as that of the UWB-IR radio communication. In general, as a frequency band in which an RF circuit performs necessary operations is wider, power consumption is larger. However, since most of power supplies of radio communication apparatuses used in the sensor net system are batteries or built-in power supplies with low driving ability, it is desirable that power consumption of the radio communication apparatuses is small.
Therefore, JP-A-2005-217899 discloses a technique for reducing power consumption of a receiver for the UWB-RI radio communication system. In a method of reducing power consumption disclosed in JP-A-2005-217899, an operation of an amplifier called a low noise amplifier at a first stage of a UWB radio receiver is stopped when there is no reception signal.
JP-A-9-321667 discloses a technique for reducing power consumption during standby of a receiver of the code division multiple access (CDMA) communication system. In a method of reducing power consumption disclosed in JP-A-9-321667, a matched filter to which a baseband signal demodulated from a reception signal is supplied is driven only when it is possible to detect a peak of a correlation value with a power supply voltage control circuit at predetermined time intervals during standby.
In Masashi Horiguchi et al, “Switched-Source-Impedance CMOS Circuit For Low Standby Subthreshold Current Giga-Scale LSI's”, IEEE TRANSACTIONS ON SOLID-STATE CIRCUITS, VOL. 28, No. 11, NOVEMBER 1993, PP. 1131-1135, in order to reduce a subthreshold current of a refined MOS transistor, a switch on a power supply side and a switch on a ground side that interrupt the subthreshold current are respectively connected to a power supply voltage side of CMOS inverters at a first stage and a third stage and a ground voltage side of CMOS inverters at a second stage and a fourth stage of CMOS inverter chains dependently connected in series.